The present invention generally relates to apparatuses and methods for increasing air permeability of fabrics, and in particular, to apparatuses and methods using a combination of fabric tension and mechanical treatment, and the fabrics and products resulting from the apparatuses and methods.
The goal for some types of fabric applications, such as air bags, is to produce an uncoated highly constructed, dense and strong fabric, but keep the air permeability at a desired level. For example, a waterjet woven fabric at a desired construction may have air permeability lower than a desired value when tested directly after weaving. To bring the permeability within a desired performance, the fabric can be subjected to at least one finishing process.
Heat setting has been used as a finishing process to increase air permeability, and is relatively expensive. An example of heat setting may be found in U.S. Pat. No. 5,581,856 (Krummheuer et al) which describes a technique that requires the use of a tenter dryer, or some other type of oven to be used to subject the fabric to elevated levels of heat. This oven equipment, along with the means to unroll, drive, and re-roll the fabric requires substantial costs in equipment, energy, and manpower increasing the cost to make the textile. Other methods of heat setting can make use of surface contact cans in place of an oven.
Stationary breaker bars have been used in a finishing process to soften fabric and are described in U.S. Pat. Nos. 5,966,785 and 6,195,854. The breaker bars do increase the softness of the fabric, but have the disadvantage that when multiple edges are used, the tension drag on each edge is accumulative and may increase beyond a desirable value. This increase in tension from many breaker bars in series may cause difficulty in the downstream roll-up drive and the continual rise in tension tends to heavily skew treatment onto the final breaker bar. Furthermore, it is difficult to change the number of times a fabric is rubbed by the breaker bars without running the fabric through the system multiple times or changing out the number of breaker bars in the system, both of which are costly options.
Therefore, there is a need for a process and an apparatus to increase the air permeability of a textile web a variable set amount while maintaining the textile strength and weight. There is also a need to produce uncoated airbag fabric, and the airbags made from such fabric, without the use of costly post loom heat treatment finishing processes.